Update
 

So I’ve been driving it a week now with the old air cleaner. So what I can tell to my way of thinking was this, the old gasser type plenum I put on, cheap on eBay, sounded like to my ear and the “ear” of the knock sensor like a knock and retarding timing, causing truck to run horribly. If not looking for that sensor I would have never found the true source of overheating problems though. Add to that my son worked on it with me makes it alright. Thanks for the help.

Nice that it’s running well now. I wouldn’t have thought an intake would be causing a knock that the sensor detects. I would guess it’s more likely due to changing the manifold intake pressure for a given throttle position and that affecting your timing. I don’t understand all the things the ECM uses to adjust timing and fuel but pretty sure manifold pressure (the MAP sensor) and throttle position are two.
Regardless, it’s running better now and you uncovered that bad cooling problem which definitely needed fixing + nice to work on something with your son. My son & I rebuilt an engine for a 65 Belair he inherited as teenager and it’s still something we enjoy together 15 years later.

Update
 

Well truck is running pretty good, after flushing with Oxalic acid, tri sodium phosphate, sodium carbonate, and then sodium bicarbonate it flushed coolant passageways very nicely. The radiator was still clogged with, solidified dex cool, and some sort of stop leak. Went with a new one by spectra from Amazon. 195 degrees pretty solid, and I think it could handle 180 stat if I get new prom. A little higher when warming up, but once the stat drops a couple times it settles in nicely.

AC runs cold but it’s a roadkill truck, so even in Las Vegas, I am not really gonna use it. If my wife is in the truck I need to justify the money spent so it will be on. Still a little hesitation here and there occasionally. Thinking one day I will replace the injections with new ac delco, but I can live with for now.

just still boggles my mind that the frequency of that knock sensor was the same as those injectors pinging. I noticed the same thing when I first hit my ac, it’s kinda noisy, the truck stumbles for a few seconds.

Son went through all the wheels and brakes. Cleaned off tons of old grease. Lots of cracked boots, but he zerked them all. Leaking I think through rear axle bearing, lots of grease in drum, but hey, it’s a drum. Replaced the Schroeder valve with one from an old bike tube to fix the spare. Ready for a camping road trip last week end of July. Had a choice today, relax, or take a weekend that I am not working on it just to do the headers. My son made the choice, he is dying to hear them. I have had them for six months and never had time to
do them. My son said it should take an hour. Lol. To be 13 again. Last night took us 3 hours to get our respective sides done. Just gotta put them on now. I asked my son what were the odds they just fit perfectly, no hammer or grinder at all. He said pretty good. Lol. To be 13 again.

Only code I get is egr when I’m using cruise control and hit brake. It’s lack of back pressure cuz of cherry bomb, but does not seem to effect anything. Read allot on knock sensor. Lots of information out there. There are two types of them
and they need to be tested differently. I made that mistake and bought a new one thinking the old one was bad. Although the voltage of the old one had dropped it was still ok. You tube vid of first test only works with new type knock sensor. Cool little device, but quite the pain. I liked it better when there was just a drain plug there.